The present invention relates to a device for converting vehicle speed signals and a method therefore, and more particularly to such a device including a controller for converting vehicle speed signals regardless of tire radius or drive shaft reduction ratio.
In general, an electronic speedometer or tachometer which displays the speed of a vehicle determines the speed by receiving a signal from a vehicle speed sensor mounted on an output shaft of the transmission. Such a vehicle speed sensor is usually a hall-type sensor and generates rectangular pulse signals when the vehicle runs.
Typically, a reference value is set so that a speedometer indicates 60 km/hour when the drive shaft rotates at 637 rpm. For example, if the vehicle speed sensor generates eight pulses per revolution, then the pulse number which is input to the speedometer or tachometer at 60 km/hour will be 5096 (8xc3x97637).
However, physical factors that influence the measurement of vehicle speed in such an arrangement include the final reduction ratio of the drive shaft, the loaded tire radius, and the gear ratio of the speed gear set that cooperates with the drive shaft and sensor. Depending on the model or type of vehicle, the final drive shaft reduction ratio and/or the loaded tire radius may vary, even for the same engine and the same transmission. Thus, the gear ratio of the speed gear set may need to be altered such that the drive shaft still rotates at 637 revolutions per minute at 60 km/hour. In this case, however, according to the conventional vehicle speed converting devices, the speed gear set must be newly designed and manufactured whenever the model or type of vehicle on which the device is utilized is changed. Such necessary changes cause an increase in costs for developing a new speed gear set, and may also require various specifications of the transmission to be changed, thus increasing maintenance costs.
Preferred embodiments of the invention include both a device and method for converting vehicle speed signals. In one embodiment of the device, a speed gear set is configured and dimensioned to be mounted between a drive shaft and a transmission of a vehicle. A vehicle speed sensor is connected to the speed gear set to generate pulse signals corresponding to a vehicle speed and transmit the signals to an electronic speedometer or tachometer. A controller programmed to convert vehicle speed signals communicates with a switch for controlling vehicle speed signals. The controller is electrically mounted between the vehicle speed sensor and the electronic speedometer or tachometer. Preferably, the switch controls the calculation by the controller of the pulse frequency per unit speed based on a designated speed.
In a further preferred embodiment, the controller is programmed to execute series of steps for converting the vehicle speed. These steps include at least storing in a memory factors specifying the vehicle and device characteristics, setting at least one of an input and an output reference pulse number based on the factors and on measured pulses, and calculating a number of pulses to be output to the electronic speedometer or tachometer.
A method according to an embodiment of the invention also includes at least the steps recited above. In one preferred embodiment, the storing comprises storing a loaded tire radius, a final reduction ratio of the drive shaft, a gear ratio of the speed gear set, and a number of pulses per revolution of the vehicle speed sensor. The setting and calculating preferably comprises a series of steps. These steps may include setting a reference input pulse number in a unit time per unit speed, setting a reference output pulse number per unit speed based on a specified output pulse number value, measuring pulse signals input from the vehicle speed sensor, calculating a vehicle speed by comparing the reference input pulse number with the number of pulses measured per unit time, calculating the number of pulses to be output per unit time at the calculated vehicle speed, and returning to measuring the number of pulses from the vehicle speed sensor after an output of pulse signals to an electronic speedometer or tachometer.
In an alternative preferred embodiment, the storing comprises storing a designated speed for controlling vehicle speeds. In this embodiment, the setting and calculating also comprises a series of steps. These steps include setting a reference output pulse number per unit speed on the basis of a specified output pulse number value and detecting whether the switch for controlling vehicle speed signals is xe2x80x9cONxe2x80x9d. Depending on the switch setting, further steps are performed. For example, if the switch for controlling vehicle speed signals is xe2x80x9cONxe2x80x9d, steps of measuring pulse signals which are input from the vehicle speed sensor, setting a reference input pulse number per unit speed, and then detecting whether the switch for controlling vehicle speed signals is set to be in a state of the reference input pulse number as it is in an xe2x80x9cOFFxe2x80x9d state are performed. If the switch is not set to be the reference input pulse number, process flow returns to the step of detecting a state of the switch for controlling vehicle speed signals. If the switch for controlling vehicle speed signals is set to be the reference input pulse number, steps of measuring pulse signals or the number of pulses which are input from the vehicle speed sensor, calculating a vehicle speed by comparing the number of pulses measured and the reference input pulse number, calculating the number of pulses (frequency) to be output per unit time at the calculated vehicle speed, and returning to the step of detecting a state of the switch for controlling vehicle speed signals after an output of pulse signals to an electronic speedometer or tachometer are performed. Preferably the specified output pulse number value is 637 rpm at 60 km/hour.